Discharge device



April 16, 1968 G. J. BRASWELL. ET AL DISCHARGE DEVICE Filed April 2, 1965 GARY J. BRASWELL PRESTON L. JOLLY T IR ATTORNEY United States Patent 3,378,716 DISCHARGE DEVICE Gary J. Braswell and Preston L. Jolly, Owensboro, Ky assignors to General Electric Company, a corporation of New York Filed Apr. 2, 1965, Ser. No. 445,109 3 Claims. (Cl. 313-252) ABSTRACT OF THE DISCLOSURE An anode subassembly for an electric discharge device comprising a ceramic header member having an axially extending bore therethrough, and a composite anode structure having a generally tubular sheath of titanium with an outer surface portion sealed to the surface of the bore and a cylindrical molybdenum core sealed only to at least one portion of said sheath axially spaced from the portion of the sheath sealed to said ceramic.

This invention relates to a high current density electron discharge device and particularly to such a device including structure providing high heat dissipation from the anode.

At higher frequencies of operation the size of electric discharge devices and the associated electric circuits tend to become smaller. Thus, to obtain the requisite power output from the smaller devices at higher frequency, it is necessary to greatly increase the current density of the device and to optimize its efliciency. With the decreased size of the device and the higher current densities, the problem of dissipating the heat produced in the operation of the device becomes acute. It is a primary object of this invention to provide an electron discharge device having a high heat dissipation anode structure.

Another object of this invention is to provide an electron discharge device for use in a cavity resonator, which device introduces a minimum of losses in the circuit, thus providing a high Q circuit. Another object of the invention is to provide an anode structure for an electron discharge device which anode introduces a minimum of capacitance into the circuit. A further object of the invention is to provide an electron discharge device having a low grid-anode capacitance. Still another object of the invention is to provide an electron discharge device having an anode structure which has a minimum length radio frequency conductive path so as to further reduce losses and to minimize phase shifts which might result at certain frequencies. Still another object of the invention is to provide an anode structure for an electron discharge device which may be readily sealed to the ceramic envelope parts forming a vacuum tight seal. Still another object of the invention is to provide an anode structure wherein the dimensional variations, particularly of the anode with respect to the grid, in response to temperature change are minimized.

In accordance with the objects of this invention there is provided an electron discharge device having anode which is a composite structure with a core of high thermal conductivity material surrounded by a sheath of material having subtsantially the same coefficient of expansion as the ceramic material of the envelope. A coaxial seal is provided between an outer surface portion of the sheath and a ceramic member having an axially extending bore therethrough. Further, the sheath of material is sealed to the core at a portion thereof which is axially spaced from that portion of the anode sheath which is sealed to the ceramic. It is prefered that the anode sheath extend outwardly from the discharge device to provide a radio frequency terminal connection.

The subject matter which is regarded as the invention 3,378,716 Patented Apr. 16, 1968 is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and mode of operation together with further objects and advantages may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like referenced characters refer to like elements and in which:

FIGURE 1 is a side elevation partly in section of an electron discharge device embodying the invention;

FIGURE 2 is a section view of a portion of the tube in accordance with another embodiment of the present invention; and

FIGURES 3, 4, and 5 are section views of the anode subassembly portion of an electron discharge device in accordance with other embodiments of the invention.

In the embodiment illustrated in FIGURE 1 the envelope of the electron discharge device 10 is made up of generally circular or annular metal and insulating members alternately arranged and bonded together to provide the evacuated hermetically sealed envelope. The device 10 includes a generally cylindrical composite anode 12, annular grid terminal 14 connected to grid 15, annular cathode terminal 16 connected in any conventional manner to a cathode 17, and heater pins 18 as the conductive members of the envelope. The envelope of the device further includes an annular ceramic insulating spacer member 20 interposed between and sealed to the grid terminal 14 and the cathode terminal 16. The ends of the envelope are substantially closed by ceramic header members 22 and 24. The heater pins 18 are sealed into and extend through the header member 22 for providing conductive leads to the cathode heater (not shown) in a manner well known in the art. The ceramic header 24 is provided with an axially extending bore 26 with a hermetic seal 28 formed between the inner surface of the bore 26 and an outer surface portion of the composite anode 12. For the purpose of illustrating the seal 28, a readily apparent thickness of material has been shown, but it will be appreciated that no such layer would be observed in the actual device unless under great magnification.

The composite anode structure 12 includes a core 30 of high heat conducting material substantially surrounded by a sheath 32 of material having substantially the same expansion characteristics as the ceramic header member 24. The core 30 is provided with a circumferentially extending outwardly directed flange 34, the lower surface of which forms the active anode face 36 of the electron discharge device. The anode face 36 is positioned in closely spaced parallel relation to the grid 15 and the face of the cathode 17. A hermetic seal 38 is provided between the lower end surface of the sheath 32 and the upper surface of the flange 34.

In the practice of the invention the ceramic parts are of a forsterite ceramic material and the anode core 30 is preferably of molybdenum, molybdenum being typical of the refractory metals that can be used and having the required relatively high thermal conductivity. It has not been feasible to make a reliable hermetic seal directly between the molybdenum anode core and the ceramic header 24 since the expansion characteristics of the two materials are widely different. Therefore, the sheath 32 is preferably of titanium, which has a thermal expansion characteristic substantially equal to that of the ceramic. To keep the grid-anode capacitance of the tube relatively low, an outer surface portion of the titanium sheath 32 is sealed, as at 38, to the inner surface of the bore 26. The seal may be produced by interposing a bonding shim or washer of copper or nickel between the members in a manner described and claimed in Beggs Patent No. 2,857,663 dated Oct. 28, 1958 and assigned to the assignee of the present invention, forming the coaxial seal 28. To compensate for the different expansion characteristics of the core material 30 and the sheath material 32, the hermetic seal 38 is formed between portions of the anode core and the anode sheath which are axially spaced from the portion of the sheath which is sealed to the header member 24 and a space 40 provided between the outer surface of anode core 30 and the inner surface of anode sheath 32 in the region of the coaxial seal 28, thus providing a strain relief therebetween. It will be appreciated that the space 40 may be dimensionally very small, for example, of the order of of a mil, the important criterion being that the anode core not be sealed to the anode sheath in the region of the coaxial seal 28. With the anode only connected at seal 28, the anode grid spacing is substantially constant irrespective of temperature variations.

In use, the radio frequency connection may be made to the anode 12 through the core portion which extends upwardly out of the tube, thus providing a somewhat extended path for these currents, or the radio frequency connection may be made directly to the exposed surface of the anode sheath 32. Thus, in the embodiment of the invention illustrated in FIGURE 2, a tubular anode sheath 42 is provided which extends axially above the header member 24 and greatly facilitates the making of the radio frequency connection to the sheath. In this embodiment, a cylindrical anode core 44 extends axially of the sheath 42 and is hermetically sealed thereto by a seal 46 which is axially spaced from the seal 28 between the header 24 and the sheath 42. It will be noted that in this embodiment the radio frequency path will be directly along the smooth outer surface of the sheath 42 thereby obviating any electrical discontinuity which can introduce additional reactance and loss in the circuit. A space 48 is provided between anode core 44 and anode sheath 42 to provide the necessary strain relief.

In the embodiment shown in FIGURE 3, the header member 24 is connected by hermetic seal 28 to a sheath 50. In this embodiment the anode sheath St) is provided with a pair of circumferentialiy extending inwardly directed flanges 52 and a hermetic seal 54 is formed between these flanges and anode core 56 at points axially spaced both above and below the seal 28 with strain relief being provided by the space 58.

In the embodiment shown in FIGURE 4, the header member 24 is connected by the hermetic seal 28 to a tubular sheath 60. The anode core 62 is generally I-shaped in cross section providing a space 64 between the inner surface of the anode sheath 60 and the core 62 in the region of hermetic seal 28. The core 62 is connected to the core sheath 60 by hermetic seals 66 which are axially spaced both above and below the seal 28.

In the modification shown in FIGURE 5, the header 24 is connected by hermetic seal 28 to anode sheath 68. The 'anode sheath 68 is provided :with a circumferentially extending inwardly directed flange 70 which is internally threaded. A core 72 has a circumferentially extending outwardly directed flange 74, the lower surface of which forms the active anode face. At the upper end of the anode core 72 a threaded portion 76 is provided which is mechanioally joined with the internal threads of the flange 70. The lower portion of the anode sheath 68 is hermetically connected to the core 72 by a hermetic seal 7 8.

It will thus be seen that there is provided an electron discharge device and a high heat dissipating anode subassembly therefor which can be reliably and hermetically sealed to the ceramic insulating members of a tube envelope, which minimizes the capacitance introduced in the circuit in which the discharge device is utilized, and which provides a minimum length radio frequency path from the anode face to the exterior of the tube in accordance with the aforementioned objects of this invention. While there has been illustrated various embodiments of the invention with particularity it will be apparent to those skilled in the art the changes and modifications may be made without departing from the invention in its broader aspects and, therefore, it is intended that the appended claims shall cover all changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An ultra-high-frequency electric discharge device comprising an envelope, an anode subassembly within said envelope, said subassembly comprising an insulative member having a bore extending therethrough, and a composite anode structure comprising a tubular electrically conductive sheath having an outer surface portion intermediate the ends thereof sealed to the surface of the bore, and a high thermal conductivity anode core extending through said sheath with a part thereof projecting externally of said envelope, said core being sealed to an end portion of said sheath adjacent the active surface of said anode core, thereby to provide a high thermal conductivity path through said core to the exterior of said envelope and a smooth radio-frequency current path through said sheath.

2. The device as defined in claim 1, wherein said insulative member is of ceramic material, said sheath being of a material having a coeflicient of expansion substantially matching that of said ceramic material, and said core is of molybdenum.

3. The device according to claim 1, wherein said sheath includes a circumferentially extending inwardly directed flange at each end thereof, which flanges are hermetically sealed to the core.

References Cited UNITED STATES PATENTS 2,414,137 1/1947 Branson 313-317 X 2,857,663 10/1958 Beggs 313317 X 3,050,651 8/1962 Beggs 313-25O 2,784,337 3/1957 Barnes 313266 JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner. 

